NATURE OF THE CONTINUUM-LIMIT IN THE 2D RP2 GAUGE-MODEL - ART. NO. 074510

The RP2 gauge model which allows interpolation between the RP2 and O(3 ) spin models is studied in 2D. We use Monte Carlo renormalization tec hniques for blocking the mean spin-spin interaction [A] and the mean g auge field plaquette [P]. The presence of the O(3) renormalized trajec tory is verified and is consistent with the known three-loop beta func tion. The first-order ''vorticity'' transition observed by Solomon et al. is confirmed, and the location of the terminating critical point i s established. New scaling flows in ([A],[P]) are observed associated with a large exponent kappa in the range 4-5. The scaling flows are fo und to give rise to a strong crossover effect between regions of high and low vorticity and are likely to induce an apparent signal for scal ing in the crossover region which we propose explains the scaling obse rved for RP2 and RP3 models by Caracciolo et al. and also in a study o f the SO(4) matrix model by Hasenbusch and Horgan. We show that the si gnal for this ''pseudo'' scaling will occur for the RP2 spin model in the crossover region which is precisely the region in which computer s imulations are done. We find that the RP2 spin model is in the same un iversality class as the O(3) spin model, but that it is likely to requ ire a very large correlation length before the true scaling of this cl ass sets in. We conjecture that the scaling flows are due either to th e influence of a nearby new renormalized trajectory or to the ghost of the Kosterlitz-Thouless trajectory in the associated XY model. In the former case it is argued that the ''vorticity'' fixed point controlli ng the critical behavior terminating the first-order line cannot be id entified with the conjectured new renormalized trajectory. [S0556-2821 (98)02317-0].